One of the first steps in the brewing of beer is a process known as “mashing,” in which a mix of milled grain, typically all or mostly malted barley, is combined with water and the resulting mixture is heated. The liquid extracted from the mashing process, known as “wort,” is then placed in a fermenter, where brewing yeast converts the sugars in the wort to ethanol. In the initial stages of fermentation, the yeast cells reproduce rapidly and produce excess quantities of α-acetolactate (AAL), which then undergoes a decarboxylation reaction to produce butane-2,3-dione, known to brewers as “diacetyl,” and carbon dioxide. If fermentation is allowed to proceed long enough for the yeast's primary food source, i.e. the sugars in the wort, to become scarce, the yeast will slowly reabsorb the diacetyl.
Diacetyl has a very distinctive and intense buttery flavor. In some styles of beer, a buttery flavor can be part of the intended flavor profile and low to moderate levels of diacetyl are considered acceptable or even desirable; in many other styles, however, butter is considered an “off” flavor and the presence of diacetyl is considered a serious flaw in the beer. Elevated diacetyl levels can also indicate bacterial contamination of brewing equipment. Monitoring the concentration of diacetyl in the beer is thus necessary for control of the fermentation process and so is of paramount importance to the brewer.
Methods for monitoring the diacetyl level in beer which have previously been known and described in the art have generally utilized either gas chromatography (GC) or field asymmetric ion mobility spectrometry (FAIMS). To be most effective, these processes often require samples of the beer to be processed and loaded, and many breweries, especially smaller ones, frequently opt to send samples to third-party laboratories for analysis. As a result, measuring diacetyl levels in the beer can often be quite time-consuming, which can subject the wort to a longer fermentation time than the brewer would consider optimal. In addition, these methods typically require that diacetyl measurements be taken at discrete times during fermentation, rather than allowing the brewer to monitor diacetyl levels in the beer more continuously throughout fermentation.
Many technologies for monitoring the beer fermentation process have previously been known and described in the art, but each has a significant drawback and/or a lack of an important and useful functionality. For example, PCT Application Publication No. 2015/032551, entitled “Method and apparatus for beer fermentation,” published 12 Mar. 2015 to Nordkvist et al. (“Nordkvist”), describes a method for beer fermentation, comprising the steps of inserting wort and yeast into a vessel to initiate a fermentation process, the wort and yeast forming a vessel content; measuring, with an online measuring device, a first extract value that is representative of an extract level of the vessel content; and automatically controlling a mixing device, dependent on the first extract value, to withdraw vessel content from the vessel and re-inject it into the vessel for effecting mixing of the vessel content. The method monitors and controls the beer fermentation process by using an on-line measuring device.
European Patent Application Publication No. 1,298,197, entitled “Method and apparatus for treating mash,” published 2 Apr. 2003 to Nowrouzi (“Nowrouzi”), describes a brewing process in a closed fermentation vat with a mash charge, comprising generating a gas containing carbon dioxide, wherein a measured carbon dioxide value is used as a temperature control parameter.
IR-ATR measurements have been used for the assessment of the concentration of CO2 in a liquid. For example, European Patent No. 1,903,329, entitled “An apparatus and method for optically determining the presence of carbon dioxide,” issued 22 Dec. 2010 to Tavernier et al. (“Tavernier”), describes an apparatus for optically determining the presence of carbon dioxide within a fluid.
There is a long-felt need for in-line methods of monitoring diacetyl concentration in beer during fermentation that are sufficiently robust and sensitive to enable precise control over fermentation and thereby improve the efficiency of the brewing process and the consistency and quality of the beer produced. It is further advantageous that such methods be rapid, accurate, and inexpensive, or at least significantly less costly than laboratory analysis. It would be desirable that these methods do not destroy the beer sampled or contaminate the fermenting wort.